Cheaper, longer lasting battery packs

Dr. Ngalula Mubenga, assistant professor of electrical engineering technology at The University of Toledo, holding a battery cell next to the bilevel equaliser

An electrical engineer at The University of Toledo (UT) claims to have developed an energy storage solution that makes battery packs in electric vehicles, satellites, planes and grid stations last longer and cost less.

Dr. Ngalula Mubenga, assistant professor of electrical engineering technology at UT, has called the technology a ‘bilevel equaliser’. According to Dr. Mubenga, this creation is the first hybrid that combines the high performance of an active equaliser with the low cost of the passive equaliser.

"It's a game changer because we solved the weak cell issue in lithium ion battery storage for packs with hundreds of cells," says Dr. Mubenga. "Whenever we are talking about batteries, we are talking about cells connected in a series. Over time, the battery is not balanced and limited by the weakest cell in the battery."

Previously, battery makers and automotive manufacturers have balanced the cell voltages in a large battery pack using either a passive circuit, causing more energy loss, or an active circuit, which is expensive.

"In spite of their significant losses, passive equalisers are used in most applications because they are relatively simple and low cost," Mubenga continues.

With the bilevel equaliser, the cells are grouped into sections. Each cell within the section is balanced by a passive equaliser, while the entire section is balanced by an active equaliser.

"If there are 120 cells in a battery, divide the cells into 10 groups of 12," Dr. Mubenga says. "Then you only need 9 active equaliser units and 120 passive equaliser units using the bilevel equaliser. With current active equalisers, manufacturers would have to use 120 active equalisers. For manufacturers that can't afford to use only active equalisers, the bilevel equaliser is the solution to the problem."

According to Mubenga, experiments have shown that the bilevel equaliser increases the discharge capacity of lithium ion batteries by about 30% and the pack lasts longer because the cells are balanced.

"Instead of an electric vehicle's battery lasting only four years, it would last much longer," Mubenga contends.

Mubenga and her team is licensing the hybrid equaliser and retrofit kit to manufacturers.